Superconducting and structural properties of mechanically exfoliated Fe(Se,Te) films

Thin films differ mainly in two ways from bulk single crystal samples in general: the defect density and the strain states. Due to the growth process, superconducting films contain usually many more growth defects than single crystals, such as threading dislocations, twin or anti-phase boundaries and precipitates which heavily influence and improve critical current densities due to the abundance of strong pinning centres. On the other side, epitaxial films are often strained up to a certain thickness and often even above due to the epitaxial strain within the plane of the interface leading to the opposite strain along the perpendicular direction, often the materials c-axis. These finite strain states often lead to a significant shift in the critical temperature Tc in Fe-based superconductors (FBS).
In order to disentangle these two effects and to be able to compare FBS single crystals and thin films properly, we have attempted and achieved to exfoliate thin films of Fe(Se,Te) from their CeO2-buffered SrTiO3 substrates by two methods, mechanical inductance of the structural avalanche, and adhesive cleavage at or slightly above the interface. ... mehrThe structural and superconducting properties of the exfoliated films prepared by these two methods are compared among each other as well as to single crystal data.